The present invention relates to a piston pump for supplying pressure fluid into a hydraulic consumer of an electronically controlled vehicle brake system. This consumer may principally concern at least one vehicle brake, or a master cylinder, or a pressure fluid reservoir, or a pressure fluid accumulator. A supply of several of the mentioned consumers or a supply of combinations of the mentioned consumers is basically possible.
In prior art piston pumps a piston is movably arranged in a stepped bore of an accommodating member. The piston is guided directly in the accommodating member, and non-return valves are provided which are used for the ventilation of a working chamber. The working chamber is limited by the piston. A resetting spring is supported in the working chamber on the piston between an abutment and a spring retainer. The stepped bore is isolated from the ambience by means of a closing member.
EP 0 734 494 B2 discloses a piston pump whose piston is guided directly in the pump housing. The spring cage for the valve components is configured as a sheet-metal shaped part in such a fashion that the piston, the resetting spring, and a valve subassembly are secured in relation to each other as a subassembly which can be handled independently. This special provision renders it possible to rationalize a bushing which brings about the cohesion of the components of a piston pump.
However, the piston pump according to EP 0 734 494 B2 suffers from the major shortcoming that its axial overall length needs improvement. The degree of miniaturization is not sufficient. One reason therefor can be seen in that pump piston and non-return valves are serially arranged in an axial direction. Further, the special function of the spring cage necessitates an axial attachment portion which extends externally over a front part of the pump piston and engages radially from the outside into a groove of the pump piston in positive engagement therewith. The sealing means must be arranged at an axial distance from the piston end. Finally, the support of the resetting spring on the piston needs improvement because the clip-type attachment of the resetting spring on the spring cage requires the spring cage to be tolerated with high precision and, also, the spring diameter to be tolerated with high precision. This increases the costs of manufacture because especially the resetting spring is a thermally treated metal component which suffers from inevitable changes in dimension due to this heat treatment. To permit a safe cohesion of the related components, it is necessary to tolerate the manufacture to the spring cage with high precision.
An object of the invention is to provide a piston pump having a reduced axial overall length while the support of the resetting spring is improved, and wherein the essential components of the piston pump can nevertheless be mounted in a simple fashion into an accommodating member, grouped as a subassembly in the form of a cartridge.